Supramolecular Dimerization and [2 + 2] Photocycloaddition Reactions of Crown Ether Styryl Dyes Containing a Tethered Ammonium Group: Structure-Property Relationships

Article abstract of DOI:10.1021/acs.jpca.5b10758

Molecular self-assembly is an effective strategy for controlling the [2 + 2] photocycloaddition reaction of olefins. The geometrical properties of supramolecular assemblies are proven to have a critical effect on the efficiency and selectivity of this photoreaction both in the solid state and in solution, but the role of other factors remains poorly understood. Convenient supramolecular systems to study the structure-property relationships are pseudocyclic dimers spontaneously formed by styryl dyes containing a crown ether moiety and a remote ammonium group. New dyes of this type were synthesized to investigate the effects of structural and electronic factors on the quantitative characteristics of supramolecular dimerization and [2 + 2] photocycloaddition in solution. Variable structural parameters for the styryl dyes were the size and structure of macrocyclic moiety, the nature of heteroaromatic residue, and the length of the ammonioalkyl group attached to this residue. Quantum chemical calculations of the pseudocyclic dimers were performed in order to interpret the relationships between the structure of the ammonium dyes and the efficiency of the supramolecular photoreaction. One of the dimeric complexes was obtained in the crystalline state and studied by X-ray diffraction. The results obtained demonstrate that the photocycloaddition in the pseudocyclic dimers can be dramatically affected by the electronic structure of the styryl moieties, as dependent on the electron-donating ability of the substituents on the benzene ring, and by the conformational flexibility of the pseudocycle, which determines the mobility of the olefinic bonds. The significance of electronic factors is highlighted by the fact that the photocycloaddition quantum yield in geometrically similar dimeric structures varies from ≤10^-4 to 0.38. The latter value is unusually high for olefins in solution.

Full text of DOI:10.1021/acs.jpca.5b10758

Article
pubs.acs.org/JPCA
Supramolecular Dimerization and [2 + 2] Photocycloaddition
Reactions of Crown Ether Styryl Dyes Containing a Tethered
Ammonium Group: Structure−Property Relationships
,†,‡
‡
‡
‡
Evgeny N. Ushakov,* Artem I. Vedernikov, Natalia A. Lobova, Svetlana N. Dmitrieva,
§
∥
⊥
‡
Lyudmila G. Kuz’mina, Anna A. Moiseeva, Judith A. K. Howard, Michael V. Alfimov,
,‡,∥
and Sergey P. Gromov*
†Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka 142432, Moscow Region, Russian
Federation
‡
Photochemistry Center, Russian Academy of Sciences, ul. Novatorov 7A-1, Moscow 119421, Russian Federation
§
N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninskiy prosp. 31, Moscow 119991,
Russian Federation
∥
Department of Chemistry, M. V. Lomonosov Moscow State University, Leninskie Gory 1, Moscow 119991, Russian Federation
⊥Department of Chemistry, Durham University, South Road, Durham DH1 3LE, United Kingdom
*
S Supporting Information
ABSTRACT: Molecular self-assembly is an effective strategy
for controlling the [2 + 2] photocycloaddition reaction of
olefins. The geometrical properties of supramolecular
assemblies are proven to have a critical effect on the efficiency
and selectivity of this photoreaction both in the solid state and
in solution, but the role of other factors remains poorly
understood. Convenient supramolecular systems to study the
structure−property relationships are pseudocyclic dimers
spontaneously formed by styryl dyes containing a crown
ether moiety and a remote ammonium group. New dyes of this
type were synthesized to investigate the effects of structural
and electronic factors on the quantitative characteristics of
supramolecular dimerization and [2 + 2] photocycloaddition
in solution. Variable structural parameters for the styryl dyes were the size and structure of macrocyclic moiety, the nature of
heteroaromatic residue, and the length of the ammonioalkyl group attached to this residue. Quantum chemical calculations of the
pseudocyclic dimers were performed in order to interpret the relationships between the structure of the ammonium dyes and the
efficiency of the supramolecular photoreaction. One of the dimeric complexes was obtained in the crystalline state and studied by
X-ray diffraction. The results obtained demonstrate that the photocycloaddition in the pseudocyclic dimers can be dramatically
affected by the electronic structure of the styryl moieties, as dependent on the electron-donating ability of the substituents on the
benzene ring, and by the conformational flexibility of the pseudocycle, which determines the mobility of the olefinic bonds. The
significance of electronic factors is highlighted by the fact that the photocycloaddition quantum yield in geometrically similar
−4
dimeric structures varies from ≤10 to 0.38. The latter value is unusually high for olefins in solution.
1. INTRODUCTION
interactions makes it possible not only to activate this
photoreaction but also to control its selectivity. To the best
of our knowledge, the first example of molecular self-assembly
resulting in stereospecific PCA of an acyclic olefin in solution
was the formation of 2:2 complexes of a functionalized
styrylbenzothiazolium dye with Mg . Somewhat earlier,
effective photodimerization of tranilast (a cinnamic acid
derivative) induced by the 1:2 host−guest complexation with
The [2 + 2] photocycloaddition (PCA) of olefins is widely used
in organic synthesis including the synthesis of pharmaceuticals
1
,2
and natural products. Furthermore, it is one of the most
useful photoreactions in material chemistry and applied
2+
4
3
physics.
In homogeneous solutions, diffusion-controlled intermolec-
ular PCA reactions of olefins are normally characterized by very
low quantum yields due to short lifetime of the excited state
and afford mixtures of cyclobutane isomers. The self-assembly
of olefin molecules into pairs with a specific arrangement of the
reacting CC bonds via direct or mediated noncovalent
Received: November 3, 2015
Revised: November 16, 2015
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.jpca.5b10758
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The Journal of Physical Chemistry A
Article
5
γ-cyclodextrin was reported; however, no experimental
synthesis of ammonium dyes 4a−6a and model dye 5b devoid
of the ammonium group is reported for the first time.
evidence for the reaction selectivity was provided. The methods
of supramolecular chemistry applied to control the PCA of
unsaturated compounds in solution are covered most
2
. EXPERIMENTAL SECTION
6
,7
comprehensively in recent reviews.
1
13
General Methods. H and C NMR spectra were recorded
in DMSO-d using the solvent as the internal reference (δ
It is well-known that geometrical properties of supra-
molecular assemblies have a critical effect on the PCA efficiency8
and selectivity both in the solid phase and in solution;
however, the role of other factors remains poorly understood.
The molecules containing a crown ether moiety and a
remote ammonium group are able to spontaneously form
pseudocyclic dimers in solutions owing to the double
macrocycle−ammonium ion interaction involving hydrogen
6
H
1
1
2
.50 and δ 39.43). 2D H− H COSY and NOESY spectra and
C
1
13
H− C correlation spectra (HSQC and HMBC) were used to
assign the proton and carbon signals. The samples for
elemental analysis were dried in vacuo at 80 °C.
Materials. Acetonitrile (special purity grade, water content
<0.03%, v/v), doubly distilled water, 70% perchloric acid
(analytical grade), tetrabutylammonium perchlorate (special
purity grade) doubly recrystallized from ethanol, and calcium
perchlorate (analytical grade) dried in vacuo at 230 °C were
used in photochemical experiments. Commercial N-(4-
formylphenyl)aza-18-crown-6 ether, 4′-formylbenzo-18-crown-
6 ether, and 3-bromopropylamine hydrobromide were used in
the syntheses as received.
9
−12
bonds.
This feature has been used to control the
photochemistry of properly modified stilbene and styryl
13
1
4,15
dyes.
Scheme 1 shows the supramolecular reactions of
Scheme 1. Supramolecular Reactions of 4-Styrylpyridine
14
Derivative 1a
14,15
16
17
15
18
Synthesis. Compounds 1−3,
were obtained according to published procedures. Dyes 4a,
a,b, and 6a were synthesized as shown in Scheme 2. The
4b, 6b, 7a,b, and 9
5
condensation of heterocyclic salts 7a, 7b, and 8 with N-(4-
formylphenyl)aza-18-crown-6 ether in the presence of an
organic base afforded dyes 4a, 5a, and 5b, respectively.
Compounds 8, 10a,b and dye 6a were synthesized by
quaternization of lepidine, 2-methylbenzothiazole, and styr-
ylbenzothiazole 9 with iodoethane and 3-bromopropylamine
hydrobromide followed by anion exchange with perchloric acid
or NaClO . Dye 6a was also obtained by condensation of salt
4
1
13
1
0b with 4′-formylbenzo-18-crown-6 ether. The H and
NMR spectra of 4a, 5a,b, 6a, 8, and 10a,b are presented in the
C
Supporting Information (Figures S1−S14). Styryl dyes 4a, 5a,b,
3
and 6a were obtained as the E isomers ( J
= 15.7−16.2
HCCH
Hz). All of the synthesized perchlorate salts are nonexplosive
substances.
1
-(3-Ammoniopropyl)-4-{(E)-2-[4-(1,4,7,10,13-pen-
taoxa-16-azacyclooctadecan-16-yl)phenyl]vinyl}-
pyridinium Diperchlorate (4a). A mixture of compound 7a
(
130 mg, 0.37 mmol), N-(4-formylphenyl)aza-18-crown-6
ether (149 mg, 0.41 mmol), dry pyridine (1 mL), and absolute
EtOH (8 mL) was heated at 80 °C (oil bath) for 25 h. After
cooling to 5 °C, the precipitate formed was filtered off and
washed with cold absolute EtOH (2 × 3 mL) and CH Cl (5
2
2
mL). The solid was heated at 80 °C with absolute EtOH (5
mL), then cooled to 5 °C, filtered off, and dried in air to give
dye 4a (205 mg, 79% yield) as a red powder: mp 215−217 °C
styryl dye 1a in MeCN. The self-assembly of this dye and its
analogues 1b,c and 2a,b (Chart 1) into pseudocyclic dimers
was found to activate stereospecific PCA, which produces the
cyclobutane derivative as the only rctt isomer. The degree of
conversion of dyes 1a−c and 2a to the corresponding rctt-
cyclobutanes approached 100%.
Here we report the first quantitative study of the structure−
property relationships for the supramolecular pseudocyclic
dimers of styryl dyes. For a series of dyes containing a tethered
ammonium group (compounds 1−6 in Chart1), the dimeriza-
tion equilibrium constants and the quantum yields of
supramolecular PCA were measured in solutions. Quantum
chemical modeling of several dimeric complexes was performed
in order to interpret the relationships between the structure of
the ammonium dyes and the efficiency of the supramolecular
photoreaction. An X-ray diffraction study revealed that dye 4a
in the crystalline state exists as a pseudocyclic dimer. The
1
5
1
dec; H NMR (500.13 MHz, 30 °C) δ 2.15 (m, 2H,
CH CH NH ), 2.84 (br s, 2H, CH NH ), 3.54 (s, 8H, 4
2
2
3
2
3
CH O), 3.56 (m, 8H, 4 CH O), 3.63 (m, 8H, (CH ) N, 2
2
2
2 2
3
3
CH O), 4.46 (t, J = 7.1 Hz, 2H, CH N), 6.81 (d, J = 9.1 Hz,
2
2
3
2
H, 3′-H, 5′-H), 7.16 (d, J = 16.2 Hz, 1H, HCCHPy), 7.58
3
(
d, J = 9.1 Hz, 2H, 2′-H, 6′-H), 7.69 (br s, 3H, NH ), 7.92 (d,
3
3
3
J = 16.2 Hz, 1H, HCCHPy), 8.08 (d, J = 6.8 Hz, 2H, 3-H,
3
13
5
-H), 8.71 (d, J = 6.8 Hz, 2H, 2-H, 6-H) ppm; C NMR
(125.76 MHz, 30 °C) δ 28.37 (CH CH NH ), 35.72
(CH NH ), 50.59 ((CH N), 56.12 (CH N), 67.75
((CH CH N), 69.84 (2 CH O), 69.90 (2 CH O), 69.97 (4
CH
2
2
3
)
2
3
2
2
2
)
2
2
2
2
2
O), 111.64 (3′-C, 5′-C), 116.78 (HCCHPy), 122.18
2
(1′-C), 122.39 (3-C, 5-C), 130.38 (2′-C, 6′-C), 142.28 (HC
CHPy), 143.33 (2-C, 6-C), 149.99 (4′-C), 153.94 (4-C) ppm.
B
DOI: 10.1021/acs.jpca.5b10758
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Chart 1. Crown Ether Styryl Dyes 1−6
Scheme 2. Synthesis of Dyes 4a, 5a,b, and 6a
3
3
Anal. Calcd for C H Cl N O (700.56): C, 48.00; H, 6.19;
Hz, 1H, 8-H), 9.05 (d, J = 9.1 Hz, 1H, 5-H), 9.07 (d, J = 6.8
Hz, 1H, 2-H) ppm; 13C NMR (125.76 MHz, 30 °C) δ 27.05
(CH CH NH ), 36.11 (CH NH ), 50.69 ((CH ) N), 52.91
2
8
43
2
3
13
N, 6.00. Found: C, 48.07; H, 6.11; N, 5.97.
-(3-Ammoniopropyl)-4-{(E)-2-[4-(1,4,7,10,13-pen-
1
2
2
3
2
3
2 2
taoxa-16-azacyclooctadecan-16-yl)phenyl]vinyl}-
quinolinium Diperchlorate (5a). This was obtained similarly
to 4a from compound 7b (70 mg, 0.18 mmol) and N-(4-
formylphenyl)aza-18-crown-6 ether (70 mg, 0.19 mmol) in
(CH N), 67.82 ((CH CH ) N), 69.85 (2 CH O), 69.92 (2
2 2 2 2 2
CH O), 70.00 (4 CH O), 111.74 (3′-C, 5′-C), 112.90 (HC
2
2
CHHet), 114.03 (3-C), 118.51 (8-C), 122.91 (1′-C), 126.11
(4a-C), 126.66 (5-C), 128.40 (6-C), 131.61 (2′-C, 6′-C),
134.70 (7-C), 137.81 (8a-C), 145.10 (HCCHHet), 145.92
(2-C), 150.60 (4′-C), 153.58 (4-C) ppm; UV−vis (MeCN)
8
5% yield (115 mg) as a dark blue powder: mp 204−206 °C;
1
H NMR (500.13 MHz, 30 °C) δ 2.21 (m, 2H, CH CH NH ),
2
2
3
−
1
2
8
.96 (m, 2H, CH NH ), 3.55 (s, 8H, 4 CH O), 3.55−3.60 (m,
λ
(ε) = 239 (19900), 309 (12300), 558 nm (37100 M ·
max
1
2
3
2
−
H, 4 CH O), 3.66 (m, 4H, (CH CH ) N), 3.70 (m, 4H,
cm ). Anal. Calcd for C H Cl N O (750.62): C, 51.20; H,
2
2
2 2
32 45 2 3 13
3
3
(
CH ) N), 4.91 (t, J = 7.3 Hz, 2H, CH N), 6.86 (d, J = 9.1
6.04; N, 5.60. Found: C, 51.28; H, 6.01; N, 5.61.
1-Ethyl-4-methylquinolinium Perchlorate (8). A sol-
ution of lepidine (2.00 mL, 15.15 mmol) and EtI (1.83 mL,
2
2
2
3
Hz, 2H, 3′-H, 5′-H), 7.70 (br s, 3H, NH ), 7.86 (d, J = 9.1 Hz,
3
3
2
H, 2′-H, 6′-H), 7.97 (m, 1H, 6-H), 8.02 (d, J = 15.7 Hz, 1H,
3
HCCHHet), 8.19 (d, J = 15.7 Hz, 1H, HCCHHet), 8.21
22.72 mmol) in CH Cl2 (15 mL) was kept at room
2
3
3
(
m, 1H, 7-H), 8.36 (d, J = 6.8 Hz, 1H, 3-H), 8.43 (d, J = 9.1
temperature in the dark for 17 days. The solvent was
C
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1
evaporated in vacuo, and the residue was triturated with
benzene (15 mL). The insoluble fraction was filtered off,
washed with benzene (3 × 15 mL), and dried in vacuo at 80 °C
to give 1-ethyl-4-methylquinolinium iodide (3.67 g, 81% yield)
powder: mp 278−279 °C dec; H NMR (500.13 MHz, 24 °C)
δ 2.16 (m, 2H, CH CH NH ), 3.07 (m, 2H, CH NH ), 3.21 (s,
2
2
3
2
3
3H, Me), 4.81 (m, 2H, CH N), 7.82 (m, 1H, 6-H), 7.90 (br s,
3H, NH ), 7.92 (m, 1H, 5-H), 8.40 (d, J = 8.5 Hz, 1H, 4-H),
8.48 (d, J = 8.0 Hz, 1H, 7-H) ppm; C NMR (125.76 MHz,
25 °C) δ 17.15 (Me), 25.59 (CH CH NH ), 35.90 (CH NH ),
46.51 (CH N), 116.68 (4-C), 124.69 (7-C), 127.96 (6-C),
129.12 (7a-C), 129.22 (5-C), 140.70 (3a-C), 177.71 (2-C)
ppm. Anal. Calcd for C H Br N S (368.13): C, 35.89; H,
.38; N, 7.61. Found: C, 35.64; H, 4.31; N, 7.51.
3-(3-Ammoniopropyl)-2-methyl-1,3-benzothiazol-3-
ium Diperchlorate (10b). Compound 10a (507 mg, 1.38
mmol) was dissolved at heating in a mixture of MeOH (12 mL)
and water (0.3 mL). A solution of NaClO (408 mg, 3.32
mmol) in MeOH (1 mL) was added to the solution of
compound 10a, and the reaction mixture was cooled to −10
°C. The precipitate formed was filtered off, washed with cold
absolute EtOH (2 × 5 mL), and dried in air to give compound
0b (510 mg, 91% yield) as light-beige crystals: mp 257−258
C dec; H NMR (500.13 MHz, 26 °C) δ 2.12 (m, 2H,
CH CH NH ), 3.04 (m, 2H, CH NH ), 3.18 (s, 3H, Me), 4.76
m, 2H, CH N), 7.76 (br s, 3H, NH ), 7.83 (m, 1H, 6-H), 7.93
2 3
2
3
3
19
3
13
as a yellow-green powder: mp 142−143 °C (lit.: mp 143−144
1
3
°
(
(
C); C NMR (125.76 MHz, 25 °C) δ 15.10 (MeCH ), 19.60
2
2
2
3
2
3
MeHet), 52.39 (CH N), 119.10 (8-C), 122.66 (3-C), 127.05
5-C), 128.77 (4a-C), 129.43 (6-C), 134.97 (7-C), 136.41 (8a-
2
2
C), 147.96 (2-C), 158.23 (4-C) ppm. The iodide salt (1.08 g,
.61 mmol) was dissolved at heating in a minimum quantity of
11
16
2
2
3
4
absolute EtOH. After the addition of 70% HClO (aq) (0.29
4
mL, 3.34 mmol) and cooling to −10 °C, the precipitate formed
was filtered off, washed with cold absolute EtOH (2 × 3 mL),
and dried in air to give compound 8 (0.38 g, 39% yield) as a
4
1
light yellow crystalline powder: mp 128−130 °C; H NMR
3
(
(
6
(
(
°
(
500.13 MHz, 30 °C) δ 1.59 (t, J = 7.3 Hz, 3H, MeCH ), 3.00
2
3
s, 3H, MeHet), 5.04 (q, J = 7.3 Hz, 2H, CH N), 8.05 (m, 1H,
-H), 8.06 (d, J = 6.6 Hz, 1H, 3-H), 8.26 (m, 1H, 7-H), 8.55
d, J = 8.6 Hz, 1H, 5-H), 8.59 (d, J = 9.1 Hz, 1H, 8-H), 9.39
d, J = 6.6 Hz, 1H, 2-H) ppm; C NMR (125.76 MHz, 26
C) δ 15.09 (MeCH ), 19.54 (MeHet), 52.43 (CH N), 119.10
2
3
3
3
1
°
3
13
1
2
2
2
2
3
2
3
8-C), 122.72 (3-C), 127.09 (5-C), 128.85 (4a-C), 129.48 (6-
(
(
C), 135.03 (7-C), 136.50 (8a-C), 148.01 (2-C), 158.35 (4-C)
ppm. Anal. Calcd for C H ClNO (271.70): C, 53.05; H,
3
3
m, 1H, 5-H), 8.34 (d, J = 8.6 Hz, 1H, 4-H), 8.46 (d, J = 8.2
Hz, 1H, 7-H) ppm; C NMR (125.76 MHz, 25 °C) δ 16.82
13
1
2
14
4
5
.19; N, 5.16. Found: C, 53.08; H, 5.14; N, 5.09.
(
1
1
Me), 25.65 (CH CH NH ), 36.01 (CH NH ), 46.34 (CH N),
2 2 3 2 3 2
1
-Ethyl-4-{(E)-2-[4-(1,4,7,10,13-pentaoxa-16-azacy-
16.49 (4-C), 124.66 (7-C), 128.08 (6-C), 129.17 (7a-C),
29.29 (5-C), 140.71 (3a-C), 177.79 (2-C) ppm. Anal. Calcd
for C H Cl N O S (407.22): C, 32.44; H, 3.96; N, 6.88.
Found: C, 32.51; H, 4.07; N, 6.81.
-(3-Ammoniopropyl)-2-[(E)-2-(2,3,5,6,8,9,11,12,-
4,15-decahydro-1,4,7,10,13,16-benzohexaoxacyclooc-
tadecin-18-yl)vinyl]-1,3-benzothiazol-3-ium Diperchlo-
rate (6a). Method A. A mixture of compound 9 (150 mg,
0.32 mmol) and 3-bromopropylamine hydrobromide (209 mg,
0.96 mmol) was heated at 150 °C (oil bath) in the dark for 4 h.
The reaction mixture was extracted with hot absolute EtOH (3
× 5 mL, cooling to −10 °C before decantation). The insoluble
fraction (171 mg) was dissolved at heating in a mixture of
EtOH (10 mL) and water (several drops). After the addition of
70% HClO (aq) (95 μL, 1.18 mmol) and cooling to −10 °C,
the precipitate formed was decanted and recrystallized from
aqueous EtOH (5 mL) containing 70% HClO (aq) (45 μL,
0.56 mmol). The solid was filtered off, washed with absolute
EtOH (5 mL), and dried in air to give dye 6a (53 mg, 22%
overall yield) as an orange powder: mp 250−252 °C; H NMR
500.13 MHz, 25 °C) δ 2.14 (m, 2H, CH CH NH ), 3.00 (m,
H, CH NH ), 3.54 (s, 4H, 2 CH O), 3.57 (m, 4H, 2 CH O),
2 3 2 2
.64 (m, 4H, 2 CH O), 3.80 (m, 2H, CH CH OAr), 3.83 (m,
clooctadecan-16-yl)phenyl]vinyl}quinolinium Perchlo-
rate (5b). A mixture of compound 8 (200 mg, 0.74 mmol),
N-(4-formylphenyl)aza-18-crown-6 ether (300 mg, 0.81
mmol), dry piperidine (40 μL), and MeOH (10 mL) was
heated at 70 °C (oil bath) for 27 h. The solvent was evaporated
in vacuo, and the residue was washed with hot benzene (4 × 20
mL) and absolute EtOH (2 × 10 mL). The insoluble fraction
was decanted and dried in air to give dye 5b (430 mg, 94%
11
16
2
2
8
3
1
1
yield) as a dark violet glassy solid: mp 86−88 °C; H NMR
3
(
8
(
2
500.13 MHz, 30 °C) δ 1.56 (t, J = 7.1 Hz, 3H, Me), 3.54 (s,
H, 4 CH O), 3.55−3.58 (m, 8H, 4 CH O), 3.64 (m, 4H,
2
2
3
CH CH ) N), 3.67 (m, 4H, (CH ) N), 4.90 (q, J = 7.1 Hz,
2 2 2 2 2
3
3
H, CH N), 6.83 (d, J = 8.9 Hz, 2H, 3′-H, 5′-H), 7.82 (d, J =
2
3
8
.9 Hz, 2H, 2′-H, 6′-H), 7.94 (m, 1H, 6-H), 7.96 (d, J = 15.7
3
4
Hz, 1H, HCCHHet), 8.13 (d, J = 15.7 Hz, 1H, HC
3
CHHet), 8.17 (m, 1H, 7-H), 8.31 (d, J = 6.7 Hz, 1H, 3-H),
3
3
4
8
9
3
.40 (d, J = 8.7 Hz, 1H, 8-H), 8.98 (d, J = 8.7 Hz, 1H, 5-H),
3
13
.11 (d, J = 6.7 Hz, 1H, 2-H) ppm; C NMR (125.76 MHz,
0 °C) δ 14.87 (Me), 50.65 ((CH ) N), 51.26 (CH N), 67.80
2
2
2
1
(
(CH CH ) N), 69.83 (2 CH O), 69.91 (2 CH O), 69.98 (4
2 2 2 2 2
(
CH O), 111.63 (3′-C, 5′-C), 112.94 (HCCHHet), 114.11
2 2 3
2
2
3
2
(
3-C), 118.51 (8-C), 122.88 (1′-C), 125.97 (4a-C), 126.49 (5-
C), 128.30 (6-C), 131.41 (2′-C, 6′-C), 134.61 (7-C), 137.52
2
2
2
3
H, CH CH OAr), 4.23 (m, 4H, 2 CH OAr), 4.98 (t, J = 7.3
(
1
3
8a-C), 144.57 (HCCHHet), 145.63 (2-C), 150.40 (4′-C),
2
2
2
3
Hz, 2H, CH N), 7.18 (d, J = 8.6 Hz, 1H, 5′-H), 7.65 (br s, 1H,
53.12 (4-C) ppm; UV−vis (MeCN) λ (ε) = 236 (23500),
2
max
−1
3
−1
2
7
7
8
′-H), 7.69 (br d, J = 8.6 Hz, 1H, 6′-H), 7.71 (br s, 3H, NH ),
07 (13100), 542 nm (28700 M ·cm ). Anal. Calcd for
3
3
.78 (d, J = 15.7 Hz, 1H, HCCHHet), 7.80 (m, 1H, 6-H),
C H ClN O (621.12): C, 59.95; H, 6.65; N, 4.51. Found: C,
31
41
2
9
3
.90 (m, 1H, 5-H), 8.23 (d, J = 15.7 Hz, 1H, HCCHHet),
5
9.87; H, 6.51; N, 4.58.
-(3-Ammoniopropyl)-2-methyl-1,3-benzothiazol-3-
ium Dibromide (10a). A mixture of 2-methylbenzothiazole
1.34 mL, 10.58 mmol) and 3-bromopropylamine hydro-
3
3
.28 (d, J = 8.6 Hz, 1H, 4-H), 8.45 (d, J = 8.2 Hz, 1H, 7-H)
3
13
ppm; C NMR (125.76 MHz, 30 °C) δ 26.46 (CH
36.03 (CH NH ), 45.71 (CH N), 68.34 (CH OAr), 68.51
(CH OAr), 69.57 (CH O), 69.68 (5 CH O), 69.79 (CH O),
69.84 (CH
CH NH ),
2
2 3
(
2
3
2
2
bromide (1.55 g, 7.06 mmol) was heated at 150 °C (oil bath)
for 24 h. After cooling to room temperature, the reaction
mixture was triturated with benzene (3 × 10 mL), MeCN (3 ×
2
2
2
2
O), 110.35 (HCCHHet), 112.71 (5′-C), 113.31
2
(2′-C), 116.14 (4-C), 124.30 (7-C), 125.63 (6′-C), 126.70 (1′-
C), 127.90 (7a-C), 128.14 (6-C), 129.27 (5-C), 141.10 (3a-C),
148.35 (3′-C), 149.83 (HCCHHet), 152.64 (4′-C), 172.36
(2-C) ppm. Anal. Calcd for C H Cl N O S·0.5H O
10 mL), and i-PrOH (3 × 10 mL). The insoluble substance was
filtered off, washed with i-PrOH (2 × 10 mL), and dried in air
to give compound 10a (1.95 g, 75% yield) as a light-gray
2
8
38
2
2
14
2
D
DOI: 10.1021/acs.jpca.5b10758
J. Phys. Chem. A XXXX, XXX, XXX−XXX

The Journal of Physical Chemistry A
738.59): C, 45.53; H, 5.32; N, 3.79. Found: C, 45.56; H, 5.17;
N, 3.30.
Method B. A mixture of compound 10b (80 mg, 0.20
mmol), 4′-formylbenzo-18-crown-6 ether (74 mg, 0.22 mmol),
dry pyridine (0.5 mL), and absolute EtOH (10 mL) was heated
at 85 °C (oil bath) for 34 h. After cooling to room temperature,
a yellowish orange precipitate (43 mg) was filtered off and then
triturated with absolute EtOH (2 × 2 mL) at heating. The
insoluble substance was filtered off, washed with absolute EtOH
Article
(
6a. The equilibrium constants were calculated using the
2
2
HYPNMR program.
X-ray Diffraction Crystal Structure Determination and
Crystal Data. The crystals of dye 4a were grown from a
MeCN solution, which was slowly saturated with benzene by
vapor diffusion method at ambient temperature. The single
crystal was coated with perfluorinated oil and mounted on a
CCD diffractometer [graphite monochromatized Cu Kα
radiation (λ = 1.54178 Å), ω scan mode] under a stream of
cold nitrogen. A set of experimental reflections was measured,
and the structure was solved by direct methods and refined
with anisotropic thermal parameters for all non-hydrogen
atoms. Absorption correction was applied using the SADABS
method. The hydrogen atoms were fixed at calculated positions
at C and N atoms and then refined using the “riding” model.
Data for 4a. C H Cl N O , M = 700.55, monoclinic,
(
2 × 0.5 mL) and dried in air to give dye 6a (31 mg, 21% yield)
as a yellowish orange powder: mp 252−253 °C.
Dimerization Equilibrium Constants. The supramolecu-
lar dimerization of ammonium dyes 1−4 and 6 was studied by
spectrophotometry in MeCN and MeCN−H O (94:6, v/v)
2
solutions at an ionic strength of 0.01 M (Bu NClO as the
4
4
supporting electrolyte). The solutions contained minor
28
43
2
3
13
−5
amounts of HClO (1 × 10 M), which ruled out the possible
space group P2 (No. 4), red block, a = 9.8760(3), b =
4
1
deprotonation of the ammonium group of the dye by
nucleophilic impurities in MeCN (in experiments involving
azacrown dyes, the acid was not used). The absorption spectra
21.0048(6), c = 15.9354(5) Å, β = 92.053(2)°, V =
3
−1
3303.57(17) Å , T = 120(2) K, Z = 4, μ = 2.361 mm , ρ
calcd
−3
= 1.409 g cm , 2θ = 151.4°, 38916 reflections measured,
max
of solutions with different total dye concentrations (C = 2 ×
12594 unique (Rint = 0.0635), R = 0.0548 (10050 reflections
L
1
−6
−3
2
10
to 2 × 10 M) were measured in quartz cells with an
with I > 2σ(I)), wR = 0.1453 (all data), goodness-of-fit on F =
2
optical path length of 50, 10, 2, 1, 0.5, and 0.1 mm. The
resulting spectra were subjected to parametrized matrix
1.015, 932 parameters, min/max residual electron density =
−3
−0.35/0.73 e Å . One of the four independent perchlorate
̅
2
0,21
modeling
in terms of the dimerization equilibrium:
anions in structure 4a is disordered over two positions with an
occupancy ratio of 0.90:0.10, and the Het−CC−Ar moiety of
one of the two independent organic cations is disordered over
two positions with an occupancy ratio of 0.83:0.17. ISOR
command was applied to the atoms of the disordered groups in
order to constrain their anisotropic thermal parameters.
KD
L2 + L2+ ⇄ L2
+
4+
(1)
where L2 is the dye dication, L24+ is the dimeric complex, and
+
−1
KD (M ) is the dimerization equilibrium constant. This
2
3
method is suitable for simultaneous calculation of K and the
The calculations were performed using the SHELXTL-Plus
and Olex-2
D
24
absorption spectra of the monomer and dimer.
software. CCDC 1426657 contains the
−3
The exact C value after dilution of a 2 × 10 M stock
supplementary crystallographic data for 4a. These data can be
obtained free of charge from the Cambridge Crystallographic
Data Center via www.ccdc.cam.ac.uk/data_request/cif.
L
solution was determined from the optical density at the
wavelength where the monomer and the dimer have equal
molar absorption coefficients (per monomer). The isosbestic
point was found beforehand from the absorption spectra
measured in the absence of a supporting electrolyte and after
addition of a weighed portion of Bu NClO (an increase in the
Density Functional Theory (DFT) Calculations. All DFT
calculations were performed using the Gaussian 09 program
25
package. Geometry optimizations were carried out using the
2
6
27
B3LYP functional, the D3(BJ) dispersion correction, the 6-
4
4
2
8
solution ionic strength shifted the monomer−dimer equili-
brium toward the dimer, see Figure S15 in the Supporting
31G(d) basis set, and the C-PCM solvation model. The
fractional conformer populations in MeCN at 295 K were
estimated using the Boltzmann distribution function under the
assumption that thermal corrections to the B3LYP-D3/PCM
energies of different conformers are identical.
Information).
1
H NMR Titration. MeCN-d (water content <0.05%, v/v)
3
was used as the solvent. The dimerization constants K for
D
ammonium dyes 4a−6a were estimated by analyzing the
changes in the chemical shifts of the aromatic and ethylene
Quantum Yields of Supramolecular [2 + 2] Photo-
cycloaddition. Photochemical studies of ammonium dyes 1−
6 were conducted in MeCN solutions at an ionic strength of
0.01 M. Solutions were exposed to glass-filtered light of a high-
pressure Hg lamp (λ = 436 nm). The light intensity was
measured by chemical actinometry. The concentration of dyes
protons of dye, Δδ , induced by an incremental addition of
H
EtNH ClO , as described previously for ammonium dyes 1−
3
4
1
5
3
.
In these experiments, the C value was kept constant (∼1
L
−3 −3
×
10 or ∼5 × 10 M) and the total concentration of
−5
EtNH ClO (C ) varied from 0 to ∼50C . The Δδ values
before irradiation was about 3 × 10 M (10 mm cell, dyes with
3
4
S
L
H
−
4
were measured to an accuracy of 0.001 ppm. The experimental
log K > 7) or about 1.5 × 10 M (2 mm cell, dyes with log
D
D
dependencies of Δδ on C for different protons were globally
K < 7). The percentage of consumption of the dye in the
H
S
fitted to the complexation model represented by eqs 1 and 2:
supramolecular PCA reaction was determined using unconven-
tional photochemical method described in the Supporting
Information (Figures S16−S18).
For monomer−dimer systems that underwent no photo-
reactions other than PCA and in which the relative monomer
content in the equilibrium mixture was negligibly low, the
quantum yield of supramolecular PCA reaction, φ[2+2], was
determined from the kinetics of the absorption spectra
observed in the initial stage of dye photolysis. The time-
dependent spectra were subjected to parametrized matrix
K1
L2 + EtNH + ⇄ (L·EtNH3)
+
3+
3
(2)
These calculations were performed under the assumption that
−1
the complex stability constant K (M ) for the dicationic dye is
1
equal to that for the corresponding model dye having no
ammonium group. The K values for model dyes 4b−6b were
1
1
estimated from direct H NMR titrations with EtNH ClO and
3
4
then used as fixed parameters in the calculations of K for 4a−
D
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The Journal of Physical Chemistry A
Article
modeling in terms of the kinetic equation for irreversible
unimolecular photoreactions
ammonium dyes shown in Chart 1 (see Figures S19−S27 in
the Supporting Information). The long-wavelength absorption
band of the dimer (1a) has an asymmetric shape typical of dye
H-aggregates, which attests to stacking interactions between
(1 − 10−
εC (t)l
)
2
L
dC (t)
dt
31
L
φ[2+2]INA−1103
=
l
(3)
the chromophores. A good example of the effect of these
interactions on the spectral properties of unsaturated
compounds is provided by the stacked dimers of a function-
−2
−1
where I is the light intensity, cm s ; N is the Avogadro
A
−1
number, mol ; ε is the molar absorption coefficient of the
32
−
1
−1
alized butadienyl dye. The absorption band of dimer (1b)2
dimer at 436 nm (per monomer), M cm ; and l is the cell
length, cm.
(
(
Figure S19) has a more clear-cut asymmetry than that of
1a) . This is caused by the fact that the relatively short
For the monomer−dimer systems in which the relative
monomer content in the equilibrium mixture was rather high,
the φ[2+2] value was estimated from the formula
2
ammonioethyl spacers in dimer (1b) ensure stronger stacking
2
interactions between the chromophores.
The dimerization equilibrium constant KD and the
absorption spectra of the monomer and dimer were calculated
by global fitting of concentration-dependent spectra of the dye
to the equilibrium of eq 1 (see the Experimental Section). The
⎧
⎨
ΔC
tirΙNA 10 lA
, A = 1
D ′
L
0
(1 − 10−D0
)
φ[2+2]
=
−1
3
2 ⎩ D
0
⎫
⎭
D ′
Dir
ir
(1 − 10−Dir)⎬
log K values and the main spectrophotometric characteristics
D
+
of ammonium dyes 1−4 and 6 in MeCN and MeCN−H O
(4)
2
solutions at an ionic strength of 0.01 M are presented in Table
1.
where ΔC is the overall consumption of the dye in the PCA
L
reaction during the irradiation time t ; D and D are the total
ir
0
ir
The log K values in MeCN for some dyes that are highly
D
optical densities of solution at 436 nm before and after
prone to dimerization were estimated with the assumption that
irradiation; D ′ and D ′ are the contributions from the dimer to
0
ir
Δlog KD = log K (MeCN) − log K (MeCN−H O) is
D
D
2
the total optical densities at 436 nm before and after irradiation.
determined by the difference between the free energies of
The (D − D )/D value did not exceed 0.2.
0
ir
0
solvation of the ammonium group in the two solvents and
33
almost independent of the chromophore structure. This
assumption relies on the fact that the dimerization is driven by
the macrocycle−ammonium ion interactions. The approximate
log K values were calculated using Δlog K = 2.7 measured for
3
. RESULTS AND DISCUSSION
.1. Supramolecular Dimerization. 3.1.1. Spectrophoto-
metric Data. Figure 1 shows the absorption spectra of dye 1a
3
D
D
at different concentrations in MeCN−H O solution (94:6, v/v)
2
dye 6a.
at an ionic strength of 0.01 M.
It is noteworthy that the absorption spectra of the
pseudocyclic dimers of ammonium dyes in MeCN are almost
identical to those in MeCN−H O solution (see data for 1−3
2
and 6 in Table 1 and Figures 19−27 in the Supporting
Information). This fact suggests that in the mixed solvent, there
are no specific interactions of water molecules with the stacked
styryl moieties of the pseudocyclic dimers.
Recent investigations have demonstrated that styryl dyes
containing an N-methylbenzoazacrown ether moiety such as
model dye 3c exhibit stronger ionochromic responses to metal
cations in comparison with benzocrown- and N-phenyl-
34
azacrown-containing analogues. Therefore, it is not surprising
that compounds 3a,b, among the other ammonium dyes tested,
exhibit the largest hypsochromic shifts upon dimerization.
In MeCN, the dimerization equilibrium constants vary over a
very wide range (more than 5 orders of magnitude) depending
on the structure of the ammonium dye. The observed
Figure 1. Green curves are the absorption spectra of dye 1a at
correlations are discussed in section 3.1.5.
different concentrations in MeCN−H O solution (94:6, v/v); the
1
2
3
.1.2. H NMR Spectroscopic Data. Recently, it was shown
ionic strength of the solution was maintained at 0.01 M (supporting
electrolyte Bu NClO ). The red and blue curves are the spectra of
by NMR spectroscopy that ammonium dyes 1a−c, 2a, and 3a,b
4
4
are able to form pseudocyclic head-to-tail dimers in MeCN-
monomer 1a and dimer (1a) , respectively, as derived from global
2
15
fitting of the concentration-dependent spectra to the equilibrium of eq
d .
3
1
1.
Figure 2 shows the H NMR spectra of new ammonium dye
4a, its analogue 4b having no ammonium group, and a mixture
of 4b with EtNH ClO (the proton numbering is shown in
Styryl dyes 1−6 have a structure typical of donor−acceptor
chromoionophores demonstrating hypsochromic shifts upon
3
4
Chart 1). The signals of ethylene and most aromatic protons of
of
29,30
complexation with metal or ammonium cations.
The fact
dye 4a capable of self-complexation are shifted upfield (Δδ
H
that an increase in the concentration of 1a induces a substantial
hypsochromic effect attests to self-complexation of the dye,
namely, to the formation of pseudocyclic dimers due to the
double macrocycle−ammonium ion interaction (see Scheme
up to −0.25 ppm) with respect to the signals of model dye 4b
(Figure 2a,c). All proton signals of 4b shift downfield upon
+
coordination of EtNH
to the crown ether moiety of the dye
3
(Figure 2a,b). These facts indicate strong anisotropic effects of
15
1
). Similar spectral properties are exhibited by other
the chromophore moieties in the pseudocyclic dimer (4a)2.
F
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The Journal of Physical Chemistry A
Article
Table 1. Dimerization Equilibrium Constants (K ) and Spectrophotometric Characteristics of Ammonium Dyes 1−4 and 6 in
D
a
MeCN and MeCN−H O Solutions at an Ionic Strength of 0.01 M
2
MeCN
Δλ
MeCN−H O (96:4, v/v)
2
εmax × 10− dimer/dye
4
log KD
λmax dimer/dye
Δλ
εmax × 10−4 dimer/dye
dye
log KD
λmax dimer/dye
b
1a
1b
1c
2a
2b
3a
3b
4a
6a
7.3
378
4.6
5.4
378/404
383/409
26
26
3.07/2.64
3.17/2.96
b
8.1
383
3.5
379/404
419
25
2.94/2.85
<1.3
5.0
b
7.7
419/450
428/453
390/465
31
25
75
2.70/2.17
2.57/2.30
2.27/2.54
b
7.4
429
4.7
b
8.8
391
6.1
3.7
3.6
6.1
391/468
415/487
418/433
77
72
15
2.36/2.64
3.27/4.42
3.50/3.64
<1.3
<1.3
3.4
417/432
15
3.49/3.60
a
Supporting electrolyte, Bu NClO ; ambient temperature; λ is the long-wavelength absorption maximum, nm; Δλ = λ (dye) − λmax(dimer);
4
4
max
max
−
1
−1
b
εmax is the molar absorption coefficient at λmax (per monomer), M cm ; the K values are measured to within 10−20%. Estimated using a
difference of 2.7 between the log K (MeCN) and log K (MeCN−H O) values measured for dye 6a.
D
D
D
2
ammonium dyes 1a−3a and the corresponding model
compounds.
1
The log KD values estimated by H NMR titration are
consistent at a qualitative level with the data obtained by
spectrophotometry (see Table 1). What is most important is
that the dependences of log K on the dye structure are similar
D
for the two methods. Some discrepancies in the absolute
magnitudes of log K are attributable to the fact that in both
D
cases, the dimerization constants were calculated with certain
assumptions and that the solution ionic strength was not fixed
1
in the H NMR titration experiments.
4
−1
The constants K for dyes 4a and 5a do not exceed 10 M
D
and, therefore, they can be estimated by measuring the
1
concentration dependence of the H NMR spectrum. Figures
S30 and S31 (see the Supporting Information) show the
changes in the proton chemical shifts of these dyes, Δδ , as
H
induced by incremental increase in the dye concentration. In
both cases, as the dye concentration increases, the signals of
aromatic and ethylene protons and methylene protons of the
1
Figure 2. H NMR spectra (aromatic proton region) of (a) dye 4b,
b) a 1:22 mixture of 4b with EtNH ClO , and (c) dye 4a at a
(
3
4
−3
concentration of 5 × 10 M (500.13 MHz, MeCN-d , 25 °C).
3
ammoniopropyl group shift mainly upfield (Δδ of up to −0.51
H
ppm), while the proton signals from most crown ether CH O
2
groups shift downfield. The dependencies of Δδ on C were
H
L
fitted to a monomer−dimer equilibrium model to give log K =
D
Dyes 5a,b and 6a,b show similar spectral properties (see
Figures S28 and S29 in the Supporting Information).
Table 2 presents the dimerization equilibrium constants for
3
.7 for 4a and 3.2 for 5a. In the case of 4a, the calculated log KD
value is in good agreement with that estimated from the data of
titration with EtNH ClO . However, in the case of 5a, the log
3
4
ammonium dyes 4a−6a and the stability constants for the 1:1
KD values obtained by the two methods are considerably
different (3.2 vs 3.9). Apparently, dye 5a having more extended
conjugated system than 4a is more prone to form stacked
supramolecular assemblies with an aggregation number of >2.
Even a small presence of these assemblies at high dye
concentrations can introduce a substantial error into the
+
3
complexes of model dyes 4b−6b with EtNH , as derived from
1
H NMR titrations with EtNH ClO (see the Experimental
3
4
Section). The Table is supplemented by published data for
Table 2. Dimerization Equilibrium Constants (K ) for
D
Ammonium Dyes and Stability Constants (K ) for the 1:1
1
calculation of KD.
+
Complexes of Related Model Dyes with EtNH , as Derived
15
3
3.1.3. X-ray Diffraction Analysis. Previously, it was shown
1
a
from H NMR Titrations with EtNH ClO
3
4
that dyes 1b and 2b exist in the crystalline state as pseudocyclic
dimers and that dye 1b undergoes solid-phase PCA, which
induces single crystal-to-single crystal transformation.
Single crystals suitable for X-ray diffraction were also
obtained for the new dye 4a. The independent unit cell
components are shown in Figure 3. This is the first crystal
structure of a complex between an N-phenylaza-18-crown-6
ether and an ammonium ion.
dye
log KD
dye
log K1
b
b
3a
2a
1a
6a
5a
4a
8.2
3c
1d
2c
6b
4b
5b
3.9
b
b
8.0
3.6
b
b
7.1
3.5
c
5.9
3.9
3.6
3.5
1.9
1.7
The two organic dications in structure 4a form a head-to-tail
pseudocyclic dimer due to double macrocycle−ammonium ion
interaction. The azacrown ether moieties of the dications have
a
MeCN-d , 25 ± 1 °C; the equilibrium constants are measured to
3
b
c
within about 30%. Reference 15. Reference 17.
G
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Figure 3. Structure 4a (two independent dye molecules forming dimeric complex). Thermal ellipsoids are drawn at the 40% probability level. The
hydrogen atoms of crown ether moieties are omitted for clarity. Hydrogen bonds are drawn with dashed lines. Minor conformers of the disordered
parts are drawn with hollow lines.
38,39
extended and fairly twisted conformations. Poor preorganiza-
criteria,
this virtually rules out the possibility of solid-phase
tion of N-phenylazacrown ethers toward cation binding is one
PCA reaction.
+
of the reasons for low stability of complexes 4b·EtNH and 5b·
3.1.4. Quantum-Chemical Modeling. The various con-
formations of pseudocyclic dimers (1a) and (3a) were first
analyzed in the gas phase using the parametrized electronic
structure model developed by Laikov and implemented in the
Priroda 14 program. For the subsequent B3LYP-D3/PCM
calculations, we selected 8 symmetrical structures differing in
the conformation of the benzo(aza)-18-crown-6 ether moiety
3
+
EtNH3 and dimers (4a) and (5a) in solutions.
2
2
2
2
The lengths of the N(1)H···O(2′,4′) and N(1′)H···O(1,3,4)
hydrogen bonds are in the range of 1.94−2.20 Å, and the angles
at hydrogen atoms are 126−179°. In one macrocycle, there is
no hydrogen bond between the nitrogen atom and the
ammonium ion (the shortest N(1′)H···N(3) distance is 3.23
Å). In the other macrocycle, there is the N(1)H···N(3′)
hydrogen bond with parameters of 2.16 Å and 174°. The
40
41
(
up or dn, Chart 2), in the single-bond conformation of the
3
Chart 2. Conformer Notation
hydrogen bonding results in partial sp -hybridization of the
N(3′) atom, which reduces conjugation of its lone electron pair
with the chromophore electronic system, as indicated by the
smaller sum of the bond angles at N(3′) compared with N(3)
(
346.8(3)° vs 358.3(4)°) and by longer N(3′)−C bond
Ar
compared with the N(3)−C bond (1.405(5) vs 1.387(6) Å).
Ar
The styrylpyridinium unit of one of the independent
dications in structure 4a is disordered over two sites with an
occupancy ratio of 0.83:0.17. This disorder is often observed in
the crystals of stilbene-like compounds and is usually attributed
35−37
to pedal, or crankshaft, motion of the ethylene unit,
which
results in the dynamic coexistence of two single-bond
conformers in the same site of the unit cell.
In the disordered dication, the geometry of the chromophore
is nearly planar: the dihedral angles between the mean planes of
the pyridine and benzene rings in the predominant and minor
s-conformers are 3.5° and 3.6°, respectively. The chromophore
moiety of the ordered dication is a little incurved (without
twisting), the dihedral angle between the mean planes of the
pyridine and benzene rings being 13.6°. The mean planes of the
styrylpyridinium units of the two independent dications
intersect at a large angle (61°). In this conformation of the
dimeric complex, the stacking interactions between the
chromophores should be very weak.
chromophore (s-trans or s-cis), or in the relative orientation of
the two chromophores (syn-head-to-tail or anti-head-to-tail).
Full geometry optimizations were performed without symmetry
constraints.
The most stable syn- and anti-conformers of dimer (1a) are
2
shown in Figure 4. The relative energies and fractional
The distances between the carbon atoms of two ethylene
bonds in the dimeric complex are in the range of 4.59−5.62 Å,
and these bonds are nonparallel. According to topochemical
populations for all calculated conformers of (1a) and (3a)
are summarized in Table 3, while the Cartesian coordinates are
presented in the Supporting Information.
2
2
H
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The dimer of ammonioethyl dye 1b was modeled in the
15
symmetrical syn-(s-cis) conformation observed in the crystal.
2
The geometrical characteristics of syn-(s-cis-1b) calculated in
2
solution (Figure 5) are very similar to those found in the
Figure 5. Geometry of syn-(s-cis-1b) in MeCN, as calculated by the
2
B3LYP-D3/PCM method.
crystal. The distance between the olefinic bonds is about 3.50 Å
in the crystal and about 3.43 Å in solution. The dihedral angle
between the pyridine and benzene rings of the chromophore is
about 2° in the crystal and about 5° in solution, i.e., the
chromophore geometry is nearly planar in both cases. This fact
implies stronger stacking interactions between the chromo-
Figure 4. Most stable syn- and anti-conformers of dimer (1a) in
MeCN, as calculated by the B3LYP-D3/PCM method.
2
phores in syn-(s-cis-1b) compared to the syn-conformers of
2
(
1a)2.
Among the numerous symmetrical conformations of dimer
6a) calculated using the parametrized electronic structure
Table 3. Theoretical Data for Different Symmetrical
a
Conformers of Dimers (1a) and (3a) in MeCN
2
2
(
2
40
(
1a)2
(3a)2
model, five most probable structures were selected and
optimized by the B3LYP-D3/PCM method. Two most stable
conformers are shown in Figure 6; they have nearly the same
energy.
conformer
Erel
P
Erel
P
anti-(s-cis-dn)2
anti-(s-cis-up)2
anti-(s-trans-dn)2
syn-(s-cis-up)2
0
45.3
21.8
13.3
4.6
0.03
1.27
0
38.5
4.7
0.43
0.72
1.35
1.39
1.40
1.45
1.61
40.8
2.4
1.67
1.62
1.34
1.30
1.63
syn-(s-trans-up)2
anti-(s-trans-up)2
syn-(s-trans-dn)2
syn-(s-cis-dn)2
4.2
2.6
4.1
4.1
3.8
4.4
2.9
2.5
a
All structures are optimized by the B3LYP-D3/PCM method; E is
rel
−1
the relative energy in kcal mol ; P is the fractional population, %.
In the syn-conformers of (1a) and (3a) , the olefinic bonds
2
2
are parallel to each other, the distances between them varying
over the ranges of 3.45−3.58 Å (1a) and 3.56−3.64 Å (3a).
38,39
These geometries conform well to the criteria for PCA
and
imply the formation of syn-head-to-tail cycloadducts, in
agreement with the experimental data obtained for dye
1
4,15
1a.
The dihedral angles between the pyridine and benzene
rings of the chromophore are 15−22° for syn-(1a) and 14−22°
2
for syn-(3a) , the mean planes of the styrylpyridinium units
2
being parallel to each other.
In the most stable anti-conformers, the dihedral angles
between the pyridine and benzene rings of the chromophore
are much smaller but the mean planes of the styrylpyridinium
units intersect at a substantial angle. The CC bonds in these
structures adopt a criss-cross conformation unsuitable for PCA.
Figure 6. Most stable conformers of dimer (6a)2 in MeCN, as
calculated by the B3LYP-D3/PCM method.
The total fractional population of syn-(1a) is estimated to be
2
1
5.5%. Assuming that the quantum yield of PCA in syn-dimers
corresponds to the theoretical maximum (i.e., two), one gets
the overall quantum yield to be 0.31, which is smaller than 0.38
measured for (1a) (see section 3.2). This means that either the
The olefinic bonds in these conformers are not parallel to
each other and are shifted relative to each other in the
projection to the imaginary middle plane between the two
chromophores. The Coulomb repulsion between the benzo-
thiazolium cations may prevent these bonds from approaching
each other. The distances between the ammonium ions are
2
calculations underestimate the population of syn-(1a) or the
2
molar absorption coefficients of the syn-conformers at the
irradiation wavelength (436 nm) are higher than those of the
anti-conformers due to substantial structural differences. The
much shorter in the conformers of (6a) (8.8 and 10.5 Å) than
2
total fractional population of syn-(3a) is predicted to be 11.9%.
in the dimers of pyridinium dyes (14.5−15.4 Å). In addition,
2
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the calculated structures imply the lack of stacking interactions
between the aromatic and heteroaromatic residues.
aromatic and heteroaromatic residues and, second, by stronger
Coulomb repulsion between the NH3+ groups.
3
.1.5. Structure−Property Relationships. Analysis of the
Spacer Length. Shorter spacers in dimer (1b) compared to
2
dimerization equilibrium constants for ammonium dyes and the
stability constants for the 1:1 complexes of model compounds
with EtNH3 (Tables 1 and 2) reveals the following trends.
(1a)2 ensure stronger stacking interactions between the
pyridine and benzene rings (see B3LYP-D3/PCM calcula-
tions), which results in an increase in the dimerization
equilibrium constant. The opposite effect observed for
quinoline derivatives 2a,b is, most likely, related to the steric
interaction between the polymethylene chain and the quinoline
ring. Because of steric hindrances, the less flexible ammo-
nioethyl group in 2b is unable to adopt the conformation that
would ensure the most efficient self-complexation of the dye.
This assumption is supported by comparing the conformations
+
Macrocycle Size and Structure. The dimerization constant
KD varies depending on the crown ether moiety of the dye in
the following order: benzo-15-crown-5 ≤ N-phenylaza-18-
crown-6 ≤ N-methylbenzoaza-15-crown-5 ≪ benzo-18-crown-
6
< N-methylbenzoaza-18-crown-6. The ability of these
macrocycles to bind the primary ammonium ions varies in
the same series. This correlation is due to the fact that the
driving force for dimerization of dicationic dyes 1−6 is the
macrocycle−ammonium ion interaction. The macrocyclic
cavity size has a critical effect on the dimerization of
benzo(aza)crown ether dyes. The macrocycle geometry of
15
of dimers (1b) and (2b) in the crystal. The steric influence
2 2
of the annelated benzene ring on the dimerization of dye 2a is
less pronounced due to higher conformational flexibility of the
ammoniopropyl group.
benzo-18-crown-6 ethers is close to optimal for the formation
3.2. Supramolecular [2 + 2] Photocycloaddition. The
stationary irradiation of dye 1a in MeCN with 436 nm light
leads to fast decoloration of the solution (Figure 7), due to the
+
of three directional or six bifurcate hydrogen bonds with NH ;
3
therefore, they bind the primary ammonium ions much more
4
2,43
efficiently than benzo-15-crown-5 ether analogues.
In the case of azacrown ether dyes, the stability of
pseudocyclic dimers is also critically affected by the type of
coupling of the macrocycle with the benzene ring: the KD
constant for benzoazacrown ether 3a is 5 orders of magnitude
higher than that for related phenylazacrown ether 4a. One
reason for this huge difference in the K values is the fact that
D
N-methylbenzoazacrown ethers are better preorganized toward
34
cation binding than N-phenylazacrown ethers, in particular,
44
due to favorable orientation of the nitrogen lone pair. Yet
another and, probably, more significant reason is that the
nitrogen atom in N-methylbenzoazacrown ethers is more
3
4
basic and, therefore, it forms a stronger hydrogen bond with
+
3
NH . Owing to this feature, benzoazacrown ethers 3a,b
dimerize even more readily than analogous benzocrown ethers
1
a,c.
Nature of the Heteroaromatic Residue. The ability of the
crown ether moiety of styryl dye to bind EtNH3+ depends
weakly on the nature of the heteroaromatic core: the stability
Figure 7. Steady-state photolysis of dye 1a in MeCN with 436 nm
−
5
light; 1 cm cell, C = 2.9 × 10 M, ionic strength 0.01 M, light
L
−
6
−2 −1
intensity 8.7 × 10 einstein m c , irradiation time (min): 0, 0.7,
.5, 2.3, 3.2, 4.4, 6.2, 9.0, 14.0, and 60 (red curve). Inset: percentage of
constants K of the complexes formed by model dyes 1d, 2c,
1
1
and 6b containing pyridine, quinoline, and benzothiazole
residues are very similar. Meanwhile, analogous dyes containing
N-ammoniopropyl group (compounds 1a, 2a, and 6a) differ
significantly in the self-complexation behavior: the KD value
increases by more than an order of magnitude in the sequence
conversion of 1a as a function of the irradiation time; the solid curve is
from global fitting to eq 3.
PCA reaction. The time dependence of the conversion to the
cycloadduct in the initial stage of photolysis (inset in Figure 7)
is described by the kinetic equation for irreversible unim-
olecular photoreactions eq 3. This is due to the following
6a < 1a < 2a. The key factor responsible for these differences is
the stacking interactions between the chromophores in
pseudocyclic dimers. It has been reported that stacking can
have significant effects on both the structure and stability of
−5
factors: first, at ∼10 M concentrations, dye 1a is almost
1
1−13
dimeric complexes.
The important role of stacking
completely dimerized (log K = 7.3), second, the cycloadduct
D
interactions in the self-complexation of pyridine and quinoline
does not absorb light with λ = 436 nm; and third, the quantum
derivatives is evidenced by the fact that the log K values for
yield of E−Z photoisomerization in dimers (1a) is negligibly
D
2
ammonium dyes 1a−5a are more than twice greater than the
low as compared with the PCA quantum yield. Qualitatively
similar photochemical properties are exhibited by dyes 1b and
2a,b (Figures S32−S34 in the Supporting Information).
Table 4 presents the quantum yields of the PCA reaction in
the supramolecular dimers of ammonium dyes 1−6 in MeCN.
The dimers of styrylpyridine and styrylquinoline derivatives
having ammoniopropyl spacers, (1a) , (1c) , and (2a) ,
log K values for the corresponding model dyes.
1
The quinoline derivatives 2a and 5a form more stable dimers
in comparison with the related pyridine derivatives 1a and 4a.
The opposite situation is observed for the 1:1 complexes of
+
model dyes with EtNH . This is due to the fact that more
3
extended conjugated system in 4-styrylquinoline derivatives
leads to stronger stacking interactions in the dimeric complex.
The results of B3LYP-D3/PCM calculations imply that much
lower stability of dimers (6a) compared to (1a) and (2a) is
2
2
2
undergo this photoreaction very readily owing to favorable
relative positions and rather high mobility of the olefinic bonds
in the syn-conformers (see section 3.1.4). Comparison of the
φ[2+2] values measured for (1a) and (1c) suggests that the
2
2
2
caused, first, by the lack of stacking interactions between the
2
2
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Table 4. Quantum Yields of the [2 + 2] Photocycloaddition
Reaction in the Supramolecular Dimers of Ammonium Dyes
for several hours induced only minor changes in the absorption
spectra. The inefficiency of PCA in (4a)2 and (5a)2 is
attributable to unfavorable geometric factors related to specific
conformational properties of the N-phenylaza-18-crown-6-
crown ether moiety (see the crystal structure of dimer (4a)2
in Figure 3). It is more difficult to interpret the photochemical
inertness of dimers (3a) and (3b) containing benzoazacrown
1
−6, φ[ , and Key Spectrophotometric Characteristics of
2+2]
a
Cycloadducts
data for cycloadducts
dimer
φ[2+2]
0.38
λmax
ε × 10−
4
2
2
(
(
(
(
(
(
(
(
(
(
1a)2
1b)2
1c)2
2a)2
2b)2
3a)2
3b)2
4a)2
5a)2
6a)2
286
288
286
319
321
0.62
0.64
0.58
1.38
1.14
ether moieties. According to B3LYP-D3/PCM calculations, the
0.049
0.26
syn-conformers of (3a) differ little in the geometric character-
2
istics from the corresponding conformers of dimer (1a) , which
2
0.27
readily undergoes PCA. The distances between the parallel
0.0065
≤10−
olefinic bonds in the syn-conformers of (3a) are longer than in
2
4
(1a) but the difference is only 0.06−0.11 Å, which can hardly
2
−
−
−
4
4
4
≤10
≤10
≤10
be responsible for the contrasting difference in photoreactivity
between these dimers. The fractional populations of syn-
conformers of (1a) and (3a) are comparable in magnitude.
2
2
−4
<10
Presumably, the inefficiency of PCA in dimers (3a) and
3b) is related to fast photoinduced recoordination reaction
2
2
a
(
In MeCN; λmax is the long-wavelength absorption maximum, nm; ε is
−1
−1
the molar absorption coefficient at λmax, M cm .
typical of complexes of azacrown-containing styryl dyes with
34
monocations. The recoordination implies disruption of the
hydrogen bond between the ammonium ion and the macro-
cycle nitrogen atom immediately after electronic excitation of
the chromophore. This can be followed by nonradiative
deactivation via the TICT state or via charge transfer between
macrocycle size in the dye affects only slightly the relative
positions of the chromophores in the dimer.
Analogues of dimers (1a)2 and (2a)2 having shorter
(
ammonioethyl) spacers, (1b) and (2b) , show much lower
2 2
the two chromophores (note that dimers (3a) and (3b)
PCA quantum yields: in the case of pyridine derivatives, the
φ[2+2] value drops 8-fold, while in the case of quinoline
derivatives, it drops 40-fold. Note that distances between the
parallel olefinic bonds in dimers (1b) and (2b) in the
2
2
virtually do not luminesce).
The pseudocyclic dimers of benzothiazole derivative 6a do
not undergo PCA but, in contrast to dimers of pyridine and
quinoline derivatives, they can undergo E−Z photoisomeriza-
tion. According to B3LYP-D3/PCM calculations, the relative
positions of the olefinic bonds in the most probable conformers
2
2
1
5
crystalline state are virtually equal (3.50 vs 3.49 Å).
Furthermore, according to B3LYP-D3/PCM calculations, the
arrangement of the olefinic bonds in syn-(1b) in solution is not
2
of (6a) are unfavorable for PCA (see Figure 6); in addition,
less favorable for PCA than in syn-(1a)2.
The most likely reason for lower photoreactivity of (1b)2
2
the Coulomb repulsion between the benzothiazolium cations
can prevent these bonds from approaching to each other. In the
compared to (1a) is lower conformational flexibility of the
2
case of (6a) , photoinduced rotation around the CC double
ammonioethyl spacers restricting the mobility of olefinic bonds.
2
bond is sterically less hindered due to the specific pseudocycle
geometry, the excimer formation being unlikely because of the
lack of stacking interactions between the aromatic and
heteroaromatic residues.
In dimer (2b) , the steric interaction of the annelated benzene
2
ring of quinoline with the dimethylene chain is one more factor
reducing the conformational flexibility of the pseudocycle;
therefore, the effect of the spacer length on the dimer
photoreactivity is most pronounced for quinoline derivatives.
Note that model dye 1d undergoes E−Z photoisomerization
in MeCN with a quantum yield of 0.17, which increases upon
4
. CONCLUSIONS
This study identified the key factors determining the
thermodynamic stability and photochemical reactivity of the
pseudocyclic dimers spontaneously formed by styryl dyes
containing a crown ether moiety and a remote ammonium
group.
45
complexation of 1d with ammonium ions. Photochemical
studies of the dimer−monomer equilibrium mixtures with high
monomer contents (in MeCN−H O solutions) revealed that
2
the monomers of dyes 1a−c also undergo this photoreaction,
unlike the dimers. The inefficiency of geometric photo-
isomerization in the pseudocyclic dimers of 1a−c is apparently
due to significant steric hindrance for rotation around the C
C double bond. Yet another possible reason is rapid conversion
of the locally excited state to a delocalized excimer state,
The driving force of the supramolecular dimerization is the
double macrocycle−ammonium ion interaction; therefore, the
thermodynamic stability of dimers is critically affected by the
size and structure of the macrocyclic moiety in the dye. The N-
methylbenzoaza-18-crown-6 ether moiety provides the highest
stability of pseudocyclic dimers. A noticeable role in the self-
complexation of the dyes is played by stacking interactions. The
strength of these interactions in the dimer depends on the
nature of the heteroaromatic residue in the dye, the length of
the ammonioalkyl group attached to this residue and the
position of this group relative to the crown ether moiety. The
latter factor is very important, as it dictates the relative position
of styryl moieties in the dimer (cf. data obtained for related
pyridine and benzothiazole derivatives). A decrease in the
ammonioalkyl spacer length may increase the stability of the
pseudocyclic dimer owing to enhancement of the stacking
interactions but can also induce the opposite effect if there are
46
followed by deactivation along two pathways: [2 + 2]
cycloaddition (syn-conformers) and internal conversion to the
ground state (syn- and anti-conformers).
The monomers of azacrown ether dyes 3−5 virtually do not
undergo E−Z photoisomerization in polar solvents due to rapid
conversion of the initial excited state to the twisted internal
34,47
charge-transfer (TICT) state,
which is deactivated without
geometric isomerization. This feature is associated with strong
electron-donating ability of benzoazacrown and phenylaza-
crown ether moieties.
The irradiation of pseudocyclic dimers of azacrown-
containing dyes 3a,b, 4a, and 5a in MeCN with 436 nm light
K
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The Journal of Physical Chemistry A
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substantial steric interactions between the polymethylene chain
and substituents in the heteroaromatic residue.
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The [2 + 2] photocycloaddition in the pseudocyclic dimers is
actually unimolecular, and therefore, there is no correlation
between the dimerization equilibrium constant KD and the
reaction quantum yield φ[2+2]. The relative position of the two
olefinic bonds in the dimer is not the only factor having a
critical effect on φ[2+2]. Two other factors that can dramatically
affect the supramolecular photocycloaddition are the electronic
structure of styryl moieties, as dependent on the electron-
donating ability of the substituents on the benzene ring, and the
conformational flexibility of the pseudocycle, which determines
the mobility of the olefinic bonds. A clear demonstration of the
significance of the electronic factor is the contrasting difference
between the photoreactivities of dimers (1a) and (3a) having
(
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very similar geometrical characteristics. The inefficiency of
supramolecular photocycloaddition of dyes 3a,b is associated
with high electron-donating ability of N-methylbenzoazacrown
ether moieties. Detailed interpretation of the photochemical
inertness of (3a) and (3b) is a challenge, which may require
(7) Ushakov, E. N.; Gromov, S. P. Supramolecular Methods for
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additional experimental and theoretical efforts.
The results of this study can be used in the development of
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cycloaddition, E−Z photoisomerization, and other photo-
chemical reactions and for rational design of supramolecular
systems functioning as photoswitches, optical sensors, and so
on.
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(
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ASSOCIATED CONTENT
Supporting Information
■
(
*
S
V. Stable Supramolecular Dimer of Self-Complementary Benzo-18-
Crown-6 with a Pendant Protonated Amino Arm. Chem. Commun.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jpca.5b10758.
2
(
002, 3014−3015.
1H and 13C NMR spectra of synthesized compounds,
12) Zheng, B.; Zhang, M.; Dong, S.; Liu, J.; Huang, F. A Benzo-21-
1
spectrophotometric and H NMR spectroscopic data on
Crown-7/Secondary Ammonium Salt [c2]Daisy Chain. Org. Lett.
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supramolecular dimerization of styryl dyes, data on
photolysis of dimeric complexes, B3LYP-D3/PCM
calculated energies and Cartesian coordinates of dimeric
complexes, and electrochemical data for selected styryl
dyes and cyclobutanes (PDF)
(13) Amirsakis, D. G.; Elizarov, A. M.; Garcia-Garibay, M. A.; Glink,
P. T.; Stoddart, J. F.; White, A. J. P.; Williams, D. J. Diastereospecific
Photochemical Dimerization of a Stilbene-Containing Daisy Chain
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(14) Gromov, S. P.; Lobova, N. A.; Vedernikov, A. I.; Kuz’mina, L.
AUTHOR INFORMATION
Corresponding Authors
(E.N.U.) Telephone: +7 496 5245446. Fax: +7 496 5223507.
■
*
G.; Howard, J. A. K.; Alfimov, M. V. Stereospecific [2 + 2]
Autophotocycloaddition in the Dimeric Complex of 18-Crown-6
Ether Styryl Dye Bearing N-(3-Ammoniopropyl) Substituent. Russ.
Chem. Bull. 2009, 58, 1211−1216.
E-mail: e.n.ushakov@gmail.com.
(S.P.G.) Telephone: +7 495 9350116. Fax: +7 495 9361255.
(15) Gromov, S. P.; Vedernikov, A. I.; Lobova, N. A.; Kuz’mina, L.
*
G.; Dmitrieva, S. N.; Strelenko, Yu. A.; Howard, J. A. K. Synthesis,
Structure, and Properties of Supramolecular Photoswitches Based on
Ammonioalkyl Derivatives of Crown Ether Styryl Dyes. J. Org. Chem.
E-mail: spgromov@mail.ru.
Notes
The authors declare no competing financial interest.
2
(
014, 79, 11416−11430.
16) Atabekyan, L. S.; Vedernikov, A. I.; Avakyan, V. G.; Lobova, N.
ACKNOWLEDGMENTS
A.; Gromov, S. P.; Chibisov, A. K. Photoprocesses in Styryl Dyes and
Their Pseudorotaxane Complexes with Cucurbit[7]uril. J. Photochem.
Photobiol., A 2013, 253, 52−61.
■
(
This work was supported by the Russian Science Foundation
Project No. 14-13-00076) and by the Russian Foundation for
(
17) Vedernikov, A. I.; Kondratuk, D. V.; Lobova, N. A.; Valova, T.
M.; Barachevskii, V. A.; Alfimov, M. V.; Gromov, S. P. New Cation-
Capped” Complex of the Z-Isomer of a Crown-Containing Styryl Dye
Bearing a Long N-Ammonioalkyl Substituent. Mendeleev Commun.
007, 17, 264−267.
18) Fedorova, O. A.; Andryukhina, E. N.; Lindeman, A. V.; Basok, S.
Basic Research (studies on the self-complexation of N-
methylbenzoazacrown ether compounds). The X-ray diffraction
study of dye 4a was performed under support of the Russian
Academy of Sciences. L.G.K. thanks the Royal Society of
Chemistry for International Author Grant.
“
2
(
S.; Bogaschenko, T. Yu.; Gromov, S. P. Synthesis of Crown-
Containing 2-Styrylbenzothiazoles. Effect of Alkali Metal Cations on
the Condensation of Crown-Ether Benzaldehydes with 2-Methyl-
benzothiazole. Russ. Chem. Bull. 2002, 51, 319−325.
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DOI: 10.1021/acs.jpca.5b10758
J. Phys. Chem. A XXXX, XXX, XXX−XXX